Re: a very interesting problem of hash_map<> and map<>

John Harrison <>
Sat, 30 Jun 2007 05:15:56 GMT
newbie wrote:

Same thing g++ complains when using hash_map<>, but is happy with
map<> --I understand hahs_map is not standardized, but since the
compiler didn't complain something like 'hash_map<> not defined', I
suppose it's supported and should behave well when I used it
correctly. BUT it didn't.

Here is my code snippet:
class MyKey {
    virtual void foo() { return; }

class MyContainer {
   typedef hash_map<MyKey*, float> _elements; // (1) typedef
map<MyKey*, float> _elements;
   void Add(MyKey* key, float value) { if (_elements.find(key) !=
_elements.end() ) _elements[key] = value; }

When I compile the above code, the compiler complains something like
prototype not matched; when I replace line(1) with 'typedef
map<MyKey*, float> _elements;', everything passed.

Can you see the problem?

thanks a lot

Both versions are wrong. You define _elements as a type and then use it
as if it was a member variable. You are making a mistake somewhere by
frustrating when people do this.

If you got rid of typedef then your code would make some sense.


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